In internal combustion engines in which a combined injection system allows both an intake manifold injection and a direct injection, it is necessary to adapt the control of the injectors provided therefor. The adaptation takes place in that the injectors may be controlled in such a way that a fuel quantity predefined by an injection quantity specification is injected. The adaptation usually takes place in an operating state in which the injection takes place either entirely via the intake manifold or entirely as a direct injection. For this purpose, adaptation ranges are predefined, which define the ranges for the operating states of the internal combustion engine, in which an adaptation of an adaptation value is permitted which acts on the fuel quantity to be injected. The ascertained adaptation values are, however, always incorporated in the calculation of the fuel quantity, even if the instantaneous operating state of the internal combustion engine is outside the adaptation range.
Due to component tolerances and aging it is necessary to adapt the adaptation values used for the adaptation on a regular basis or at predefined points in time. According to the above methods, a correction or adaptation of the adaptation value takes place only if the relevant injection takes place either entirely via the intake manifold or entirely as a direct injection. If the adaptation is to be carried out at an arbitrary point in time, the operating state must be adapted so that it lies within the adaptation range. In particular, the operating state is modified in such a way that the internal combustion engine is operated almost entirely in the operating mode for which the adaptation value is to be adapted. This, however, results in that an optimized operating state of the internal combustion engine, which possibly provides a combined use of the direct injection and the intake manifold injection, must be exited. This is disadvantageous in particular for the fuel consumption, the exhaust gas composition, and the operating behavior, as may be expressed by knocking of the internal combustion engine, for example.